CN112853345A

CN112853345A - Laser preparation method of material for improving strength of steel rail welding seam

Info

Publication number: CN112853345A
Application number: CN202110015264.4A
Authority: CN
Inventors: 杨胶溪; 马文雨; 刘哲; 朱清; 武飞宇
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2021-01-06
Filing date: 2021-01-06
Publication date: 2021-05-28
Anticipated expiration: 2041-01-06
Also published as: CN112853345B

Abstract

A laser preparation method of a material for improving the strength of a steel rail weld joint belongs to the field of laser processing. The material comprises the following components: 0.25 to 0.50 wt% of C, Si: 0.80 to 2.25 wt%, Mn 0.95 to 2.10 wt%, Ni 0.90 to 4.20 wt%, Cr 8.50 to 12.50 wt%, Mo 0.75 to 3.20 wt%, V1.20 to 2.10 wt%, Al 0.50 to 1.50 wt%, and Ta 0.30 to 0.80 wt%. Also provides a preparation method thereof. According to the defects of various welding defects, low rolling fatigue strength and the like of a welding seam after seamless steel rail flash welding and aluminothermic welding, a strengthening layer with higher hardness, wear resistance and rolling bearing performance is deposited at the welding seam by laser, so that the service life of the steel rail is prolonged.

Description

Laser preparation method of material for improving strength of steel rail welding seam

Technical Field

The invention relates to a material for improving the strength of a steel rail welding seam and a laser preparation method, which are characterized in that the laser deposition performance of the material is matched in the welding seam area of a flash welding and thermite welding steel rail, and the material belongs to the field of laser processing and manufacturing.

Background

The railway steel rail is a core part of a railway line, the thermite welding and flash welding of the steel rail are important technologies for welding the seamless railway steel rail, and are one of important means for on-line welding, in-situ rush repair and broken rail rush repair of the railway line steel rail, but a plurality of welding defects can occur in a weld joint, and meanwhile, the heat treatment state is different from that of a base metal, so that the welding seam is a relatively weak link in the seamless railway.

The damage types of the welded seamless railway mainly comprise tread damage, transverse cracks, rail web longitudinal cracks and brittle fracture of fatigue cracks, the main defects of a welding seam and a heat affected zone are zonal segregation of a superheated zone, grain boundary composition segregation of the superheated zone, gray spot defects, welding seam slag inclusion and the like, the rolling fatigue strength is low, and the welding seam cracks are easy to appear. The strength, hardness, wear resistance and impact toughness of the welding line are poor, and the service life of the steel rail, the smoothness of train operation and the running safety of the train are affected. The material with matched laser deposition performance in the welding seam area of the flash welding and thermite welding steel rail can effectively improve the hardness, the wear resistance and the bearing performance, and has important significance for prolonging the service life of the steel rail and improving the running safety of trains.

The laser deposition technology is characterized in that high-energy laser beams are utilized to act on a metal substrate, molten alloy powder enters a substrate molten pool, and functional strengthening layers with different thicknesses are deposited on the surface of the substrate, and the laser deposition technology is an important research direction of a material surface modification technology. Elements such as Si, Mn, Mo, Ni, Al, V, Ta and the like are added into a Fe-based self-fluxing powder system to improve the mechanical property and the mechanical property of the welding seam strengthening material.

Disclosure of Invention

The invention relates to a material for improving the strength of a steel rail welding seam and a laser preparation method.

A laser deposition method for a steel rail welding seam strengthening material is characterized in that the laser deposition performance of the material is matched in a welding seam area of a flash welding steel rail and an aluminothermic welding steel rail, and the material comprises the following components: 0.25 to 0.50 wt% of C, Si: 0.80 to 2.25 wt%, Mn 0.95 to 2.10 wt%, Ni 0.90 to 4.20 wt%, Cr 8.50 to 12.50 wt%, Mo 0.75 to 3.20 wt%, V1.20 to 2.10 wt%, Al 0.50 to 1.50 wt%, Ta 0.30 to 0.80 wt%, and the balance Fe.

Selecting the alloy powder of the strengthening layer according to the mass percentage, wherein the diameter is about 70-150 mu m, mixing the multi-component alloy powder in a ball mill for one hour to realize the homogenization of the multi-component powder, placing the alloy powder in a vacuum drying oven, wherein the temperature of the vacuum drying oven is 80 ℃, the vacuum degree is-0.06 MPa, and the powder is dried for 12 hours.

The applicant invents the material for improving the strength of the steel rail welding seam and the laser preparation method, a U-shaped groove is processed at the steel rail welding seam, the strengthening material with matched laser deposition performance is deposited at the U-shaped groove, and the strengthening layer and the steel rail substrate present good metallurgical bonding. Adding elements such as Si, Mn, Mo, Ni, Al, V, Ta and the like into a Fe-based self-fluxing powder system to improve the mechanical property and the mechanical property of a strengthening layer, wherein the Si element is a strong replacement solid solution strengthening element, can be dissolved in ferrite to improve the strength and improve the wettability of the powder, the Cr, Si and Mo elements can improve the hardness and the wear resistance of the strengthening layer, the Mn and Al elements can refine the structure and improve the strength and the toughness of the strengthening layer, the Ni element can improve the cracking resistance, and the V, Ta element can improve the toughness and the strength of the strengthening layer, and the preparation process comprises the following steps:

selecting the strengthening layer alloy powder according to the mass percentage, wherein the diameter is about 70-150 mu m, selecting a steel rail subjected to thermite welding or flash welding, and processing a U-shaped groove at a welding seam, wherein the depth of the groove is 1.5-5 mm, and the width of the groove is 15-30 mm; the welding seam area is subjected to reciprocating scanning and local preheating in a defocusing spot amplifying mode, the laser power P is 500-700W, the diameter of a circular spot is 8-12 mm, the laser scanning speed V is 1-3 m/min, the flow of Ar gas protective gas is 20-30L/min, the scanning time is 15-30 minutes, and the preheating temperature is 300-450 ℃. And (3) performing laser deposition on the reinforced material at the groove, wherein the laser deposition process parameters are as follows: the laser power P is 1.5-4 KW, the diameter d of a circular light spot is 2-5 mm, the laser scanning speed V is 300-600 mm/min, the lapping rate is 30-60%, the powder feeding speed is 20-60 g/min, and the flow of protective gas is 15-25L/min. After the strengthening material is deposited by laser, the material in the cladding area is subjected to reciprocating scanning heating to remove stress in a defocusing spot amplification mode, the laser power P is 900-1500W, the diameter of a circular spot is 8-12 mm, the laser scanning speed V is 1-3 m/min, the heating temperature of the cladding area is 500-650 ℃, the flow of protective gas is 20-30L/min, and the scanning time is 15-30 minutes.

The reinforced layer obtained according to the invention is characterized in that: the deposited layer has high metallurgical quality, presents good metallurgical bonding with the steel rail and has no defects of pores, cracks and the like. The microstructure is distributed in a plane crystal-cell crystal-dendritic crystal manner, and the average microhardness of a deposited layer is 500HV_0.2The deposit phase comprises Fe-Cr solid solution, Fe-Ni solid solution, Cr_9.1Si_0.9、Fe₆₅Mn₈Mo₂₇And the like. The invention can realize the deposition of the strengthening layers with different thicknesses at the welding seam by multi-layer deposition, and the strengthening layers effectively improve the hardness, the wear resistance and the rolling bearing performance at the welding seam of the steel rail and prolong the service life of the steel rail.

According to the invention, the steel rail welding seam area is locally preheated by 300-450 ℃ before the strengthening material is deposited by laser, and the material in the cladding area is subjected to reciprocating scanning heating in a laser defocusing spot amplification mode after the strengthening material is deposited by the laser, so that the martensite structure formed by extremely rapid heating and cooling in the laser deposition process is effectively avoided, and the internal residual stress is removed. Hard phases such as Fe-Cr solid solution, Fe-Ni solid solution, Cr carbide dispersed and precipitated in the strengthening layer produce strengthening effect on strengthening structures, and the wear resistance and rolling bearing performance of the steel rail welding seam are improved.

After 8h of rolling bearing test, no obvious crack is found in the strengthening layer at the welding seam, the wear depth of the strengthening layer at the welding seam is small, and the strengthening layer has higher wear resistance and rolling bearing performance.

Drawings

FIG. 1 is a diagram of the preparation of a strengthening layer at a weld joint

FIG. 2 is a microstructure of a strengthening layer

FIG. 3 is SEM morphology of strengthening layer structure

FIG. 4 is a graph showing a hardness distribution curve in a direction perpendicular to a reinforcing layer

FIG. 5 is a horizontal hardness distribution curve of the reinforcing layer

FIG. 6 is a schematic diagram of the rolling load-carrying property experiment

FIG. 7 is a graph of wear depth for a rolled load sample according to one embodiment

FIG. 8 is a graph of wear depth for example two rolled load samples

FIG. 9 is a graph of wear depth for a triple roll load sample of an example

FIG. 10 is a graph of wear depth of a sample of a rolled steel rail load in an example

Detailed Description

The following further describes embodiments of the present invention with reference to the drawings, which are provided to aid understanding of the present invention and are not intended to limit the present invention.

Example one

(1) The welding seam area laser deposition performance matching material comprises the following components: 0.25% of C, Si: 0.80 wt%, Mn 0.95 wt%, Ni 0.90 wt%, Cr 8.50 wt%, Mo 0.75 wt%, V1.20 wt%, Al 0.50 wt%, Ta 0.30 wt%, Fe: 85.85 wt%. Weighing and preparing raw materials according to the mass percentage of the components, mixing the powder in a ball mill for 1 hour to realize the homogenization of multi-component powder, sieving the obtained uniform powder to obtain powder with similar particle size, placing the alloy powder in a vacuum drying oven, drying the powder for 12 hours at the temperature of 80 ℃ and the vacuum degree of-0.06 MPa, and placing the powder in a powder feeder.

(2) Selecting a bainite steel rail, carrying out thermite welding on the bainite steel rail, removing impurities such as surface oil stain and the like, and processing a shallow U-shaped groove with the depth of 1.5mm and the width of 15mm at a welding seam;

(3) the welding seam area is subjected to reciprocating scanning and local preheating in a defocusing spot amplification mode, the laser power P is 500W, the diameter of a circular spot is 8mm, the laser scanning speed V is 1m/min, the flow of Ar gas protective gas is 20L/min, the scanning time is 15 minutes, and the preheating temperature is 300 ℃. The laser deposition process parameters are as follows: the laser power P is 1.5KW, the diameter d of the circular facula is 2mm, the laser scanning speed V is 300mm/min, the lapping rate is 30%, the powder feeding speed is 20g/min, and the flow of the protective gas is 15L/min. After the strengthening material is deposited by laser, the material in the cladding area is subjected to reciprocating scanning heating to remove stress in a defocusing spot amplification mode, the laser power P is 900W, the diameter of a circular spot is 8mm, the laser scanning speed V is 1m/min, the heating temperature of the cladding area is 500 ℃, the flow of protective gas is 20L/min, and the scanning time is 15 minutes. The cladding coating obtained in this example was subjected to the following performance tests.

1. Microhardness

And (3) carrying out multi-point hardness test on the cross section of the reinforcing layer at the welding seam along the direction vertical to the reinforcing layer by using a Wilson VH1102 microhardness tester.

2. Rolling load performance test

The rolling bearing performance test is carried out by an MMG-10 type high-temperature high-speed friction wear testing machine (as shown in figure 6), the loading force is 2000N, the rotating speed is 200r/min, and the running time is 8 h.

Example two

(1) The same parts of the example are not described, but the difference is that the laser deposition performance of the weld zone is matched with the material composition ratio of 0.40 wt% of C, 1.50 wt% of Si, 1.50 wt% of Mn, 2.10 wt% of Ni, 10.50 wt% of Cr, 2.50 wt% of Mo, 1.50 wt% of V, 1.00 wt% of Al, 0.50 wt% of Ta and 78.5 wt% of Fe.

(2) The reciprocating scanning local preheating laser power P of the welding seam area is 600W, the diameter of a circular light spot is 10mm, the laser scanning speed V is 2m/min, the flow of protective gas is 25L/min, the scanning time is 20 minutes, and the preheating temperature is 400 ℃. The laser deposition process parameters are as follows: the laser power P is 2.5KW, the diameter d of the circular facula is 3mm, the laser scanning speed V is 420mm/min, the lapping rate is 40%, the powder feeding speed is 40g/min, and the flow rate of Ar gas protective gas is 20L/min. After the strengthening material is deposited by laser, the material in the cladding area is subjected to reciprocating scanning heating to remove stress in a defocusing spot amplification mode, the laser power P is 1200W, the diameter of a circular spot is 10mm, the laser scanning speed V is 2m/min, the heating temperature of the cladding area is 600 ℃, the flow of protective gas is 25L/min, and the scanning time is 20 minutes.

EXAMPLE III

(1) The same parts of the first embodiment are not described again, but the difference lies in the material component ratio matched with the laser deposition performance of the weld zone: 0.50 wt% of C, Si: 2.25 wt%, Mn 2.10 wt%, Ni 4.20 wt%, Cr 12.50 wt%, Mo 3.20 wt%, V2.10 wt%, Al 1.50 wt%, Ta 0.80 wt%, and Fe 70.85 wt%.

(2) The reciprocating scanning local preheating laser power P of the welding seam area is 700W, the diameter of a circular light spot is 12mm, the laser scanning speed V is 3m/min, the flow of protective gas is 30L/min, the scanning time is 30 minutes, and the preheating temperature is 450 ℃. The laser deposition process parameters are as follows: the laser power P is 4KW, the diameter d of the circular light spot is 5mm, the laser scanning speed V is 600mm/min, the lapping rate is 60%, the powder feeding speed is 60g/min, and the flow of Ar gas protective gas is 25L/min. After the strengthening material is deposited by laser, the material in the cladding area is subjected to reciprocating scanning heating to remove stress in a defocusing spot amplification mode, the laser power P is 1500W, the diameter of a circular spot is 12mm, the laser scanning speed V is 3m/min, the heating temperature of the cladding area is 650 ℃, the flow of protective gas is 30L/min, and the scanning time is 30 minutes.

Claims

1. A laser preparation method of a material for improving the strength of a steel rail weld joint is characterized by comprising the following steps: the material comprises the following components: 0.25 to 0.50 wt% of C, Si: 0.80 to 2.25 wt%, Mn 0.95 to 2.10 wt%, Ni 0.90 to 4.20 wt%, Cr 8.50 to 12.50 wt%, Mo 0.75 to 3.20 wt%, V1.20 to 2.10 wt%, Al 0.50 to 1.50 wt%, Ta 0.30 to 0.80 wt%, and the balance Fe; the laser deposition at the steel rail welding seam comprises the following steps:

(1) selecting a steel rail subjected to thermite welding or flash welding, and processing a U-shaped groove at a welding seam, wherein the depth is 1.5-5 mm, and the width of the groove is 15-30 mm;

(2) the method includes the steps that a defocusing spot amplification mode is adopted in a welding seam area for carrying out reciprocating scanning and local preheating, the laser power P is 500-700W, the diameter of a circular spot is 8-12 mm, the laser scanning speed V is 1-3 m/min, the Ar gas serves as protective gas, the flow rate is 20-30L/min, the preheating temperature is 300-450 ℃, then, a strengthening material is deposited at a groove by laser, and the laser deposition technological parameters are as follows: the laser power P is 1.5-4 KW, the diameter d of a circular light spot is 2-5 mm, the laser scanning speed V is 300-600 mm/min, the lapping rate is 30-60%, the powder feeding speed is 20-60 g/min, the flow of protective gas is 15-25L/min, and the scanning time is 15-30 minutes;

(3) after the strengthening material is deposited by laser, the material in the cladding area is subjected to reciprocating scanning heating to remove stress in a defocusing spot amplification mode, the laser power P is 900-1500W, the diameter of a circular spot is 8-12 mm, the laser scanning speed V is 1-3 m/min, the heating temperature of the cladding area is 500-650 ℃, the flow of protective gas is 20-30L/min, and the scanning time is 15-30 minutes.